Changing the subcellular localization of a signal transducing protein involved in disease is a novel approach for therapeutic intervention. The subcellular location of some proteins plays a critical role in the etiology of disease. A precise example of this is Bcr- Abl protein, the causative agent of chronic myelogenous leukemia (CML). When Bcr-Abl is in the cytoplasm of cells, it behaves as an oncogene, but if forced to the nucleus, it becomes an apoptotic factor. CML is a myeloproliferative disorder characterized by increased proliferation of granulocytes and their immature precursors; with a median survival time of 4 to 6 years. The goal of this study is to use our ligand responsive protein switch constructs to control the subcellular location of Bcr-Abl, and convert Bcr- Abl from an oncogene to an apoptotic factor. It has been shown that depletion of Bcr- Abl from the cytoplasm by nuclear trapping of Bcr-Abl can result in apoptosis. If Bcr-Abl can be directed to the nucleus, it can be converted from an oncogene to an apoptotic factor. Since Bcr-Abl oligomerizes with itself to form tetramers, nuclear trapping could be achieved by introducing exogenously localization-controllable Bcr-Abl. Upon ligand induction, localization controllable Bcr-Abl will oligomerize with wt Bcr-Abl and will undergo transport to the nucleus, followed by cellular apoptosis. In Aim 1 we will subclone localization controllable versions of Bcr-Abl (Bcr-Abl protein switch, PS) with a fluorescent tag and show oligomerization with wild-type (wt) Bcr-Abl, translocate to the nucleus, and cause apoptosis of Bcr-Abl positive K562 cells. Localization of Bcr-Abl PS will be monitored by fluorescence microscopy, and apoptosis will be tested using standard cell death assays. Interaction of wt Bcr-Abl with Bcr-Abl PS will be determined using an in vivo oligomerization between wt Bcr-Abl and Bcr-Abl protein switch and mammalian two-hybrid assay. Aim 2 will test the Bcr-Abl PS in Gleevec.-resistant leukemic cells similarly. Aim 3 will test and use specific promoters that allow preferential expression of Bcr-Abl PS in leukemia cells only. Aim 4 will test if Bcr-Abl PS will eradicate/diminish leukemia in a human xenograft model using Balb/C nude mice injected with human leukemia cells. Our goal is to use ligand responsive protein switch constructs to control the subcellular location of Bcr-Abl, and convert Bcr-Abl from an oncogene to an apoptotic factor. Our long-term, ultimate goal is to use localization controllable versions of Bcr-Abl (as gene therapy) for treatment of CML.